The present invention relates to an ignition device for an internal combustion engine, and particularly to a cylindrical ignition device which is received within a plug hole.
In a cylindrical ignition device which is received within a plug hole, it is necessary to provide a center core shape which effectively converts magnetic flux. Further, since a magnetic path is formed by both of a center core and a side core, it is necessary to make the side core have a cylindrical shape.
In accordance with a conventional method, as shown in JP-A-09-167709, a structure is made such that the side core is formed to have a circular pipe shape by using a silicon steel strip having a thickness of 0.2 to 0.7 mm and one slit is formed therein (which shape is, hereinafter, referred to as xe2x80x9ca C-type shapexe2x80x9d).
In the conventional shape of the center core, as shown in JP-A-09-167709, the center core is manufactured by laminating a plural pieces of silicon steel strip.
In the prior art mentioned above, when manufacturing the shape of the center core, it is necessary to perform laminating the silicon steel strips and fastening them. Further, there is such a case as an efficiency of converting the magnetic flux is reduced due to employing a fastening means such as caulking or the like.
Further, in the prior art mentioned above, two to four pieces of side cores are required, whereby the number of the parts is increased and the number of the steps of an assembling process is increased. Further, the efficiency of converting the magnetic flux is reduced in dependence on the width of a C-type slit.
An object of the present invention is to obtain an ignition device which can improve productivity for producing the ignition device while improving an efficiency of converting a magnetic flux by modifying a material and a structure of a center core.
Another object of the present invention is to obtain an ignition device which can reduce the number of parts and the number of the steps of the assembling process thereof while improving an efficiency of converting a magnetic flux by modifying a material and the structure of a side core and by modifying the shape of a case.
In order to achieve the objects mentioned above, in accordance with the present invention, there is provided an ignition device for an internal combustion engine in which there is used, as a material of a center core, a thin film amorphous silicon steel strip of not more than 0.1 mm in thickness or a crystallized silicon steel strip of not more than 0.23 mm in thickness, each of which amorphous and crystallized silicon steel strips has a flux density B8xe2x89xa71.4T at a direct current magnetizing force of 800 A/m when measured in accordance with the direct current magnetizing characteristic test prescribed in JIS C2550, Paragraph 7.2, and regarding the center core the shape thereof is formed to have a spirally wound, cylindrical shape. Accordingly, in the invention the space factor thereof is improved and the efficiency of converting a magnetic flux is improved. Further, the productivity of the ignition device can be improved by employing the spiral structure.
Further, in order to achieve the objects mentioned above, in the invention, there is provided an ignition device for an internal combustion engine in which a silicon steel strip having a thickness not more than 0.2 mm is used to reduce eddy current loss for a material of the side core and in which the shape thereof is formed to have a spirally wound, cylindrical shape. Thus, the space factor thereof is improved and the efficiency of converting a magnetic flux is improved. Further, a productivity can be improved by employing the spirally wound, cylindrical structure and the number of the steps of an assembling process can be reduced by making the parts formed in one unit.